In seismic exploration, geophysical data are obtained by applying acoustic energy to the earth from an acoustic source and detecting seismic energy reflected from interfaces between different layers in subsurface formations. The seismic wavefield is reflected when there is a difference in acoustic impedance between the layers on either side of the interface.
Marine seismic prospection is generally made with seismic streamers which are towed through water behind a recorder vessel at a water depth normally between about six to about nine meters, but can be towed shallower or deeper. The streamers integrate sensors such as hydrophones to detect seismic signals corresponding to pressure waves. Seismic sources may be also towed behind the recorder vessel. Seismic sources may be for example air gun arrays or water gun arrays or other sources known to those skilled in the seismic art.
In the following description, a seismic cable is understood to be a seismic streamer which can be maintained at a selected depth under a sea surface of a body of water (underwater position), or a cable lying on the sea bed (this last configuration is well known as Ocean Bottom array and the cables are in this case usually called Ocean Bottom Cables (OBC)).
The source may be towed behind a vessel to generate acoustic energy at varying locations or the source may be maintained in a stationary position.
The seismic cables used for the seismic prospection generally comprise sensors, such as hydrophones or geophones, distributed along the seismic cables, data transmission lines (such as copper lines traditionally) extending along the full length of the seismic cables for conveying data signals issued from the sensors, controllers also distributed along the seismic cables and adapted for operating interface between the sensors and the data transmission lines, and power supplying lines for electrically supplying the controllers and the sensors.
Such current systems have limitations in terms of number of channels, due to data rate on the data transmission lines and have also limitation in term of allowable length.
Additionally, failures of in-sea controllers/sensors can have strong effects on the system since reparation generally requests seismic cables retrieval.
Some seismic cables have been designed with architecture tolerant to partial failure of a controller, by using redundant telemetry lines or redundant power supply lines (HV rails).
In case of failure on only one of the telemetry lines on the controller, or sensors, (i.e partial failure), the controllers are able to reroute the data through the redundant (not failed) telemetry line.
In case of power supply failure on only one of the HV rails (partial failure which is short failure most often), the redundant HV rail allows the system to work properly.
But when there is total in-sea controller failure (the controller does not work anymore), the active parts of the seismic cable located after this deficient controller are lost. In consequence, acquisition of data must be stopped, the seismic cable must be retrieved and the deficient controller must be changed.